The present invention relates to an information reading device for a multitrack storage device such as a magnetic tape memory and it especially relates to an information reading device having an automatic gain control amplifier.
In a magnetic tape memory, for example, a plurality of read heads are provided in correspondence with a plurality of information storage tracks. On each of these tracks there is recorded a signal for controlling the gain of a corresponding amplifier connected to the read head. This signal is called an automatic read amplification (ARA) burst. The ARA burst region is followed by a region for storing data to be used by users. When the tape begins to be read, the ARA bursts in the tracks are read out before the data are read and the signals provided by the read heads are amplified by corresponding amplifiers whose gains are controlled automatically, so that the signals provided by the respective amplifiers may be maintained at a predetermined value. Thus, the gains of the respective amplifiers are determined by using the ARA bursts. The data following the ARA bursts in the respective tracks are read out by the corresponding amplifiers whose gains are thus determined.
It is to be noted, however, that the gains of some of the amplifiers reach abnormally high values in some cases.
For example, the ARA burst for one of the tracks may be recorded with a signal level substantially less than a normal signal level because of dust adhering to a corresponding one of the write heads, while the ARA bursts for the other tracks may be recorded at a normal signal level. The dust may be removed from the write head when data is recorded by the write head resulting in the signal level of the recorded data being at the normal level.
When the ARA burst recorded by a write head with foreign matter, such as dust adhering thereto, is read out by a read head without dust adhering thereto, the signal level provided by the read head is quite small and, therefore, the gain of the amplifier connected to the read head is increased to an abnormally high value which is too large to amplify the read out data which is recorded at a normal level, resulting in the signal waveform for the read out data being distorted by the amplifier.
In another case, the ARA burst and the data for one of the tracks may be recorded at a normal level. The signal level of the ARA burst read out by the read head may be quite small if dust adheres to the read head. The dust adhering to the read head may be removed when the data following the ARA burst is read out by the read head, and the read out data signal level is at a normal level, resulting in the gain of the amplifier being too large to amplify the data signal at the normal level without waveform distortion. The distortion of the waveform of the data signal results in incorrect detection of the data.
Therefore, an abnormally high gain of an amplifier connected to a read head must be avoided.